1. Field of the Invention
The present invention relates generally to sealed electric storage batteries, and more particularly to vent caps for such batteries which provide a flow path for the escape of hydrogen and oxygen formed during the electrochemical reaction which takes place in such batteries. Still more specifically, the invention relates to a vent cap which also controls the flow of electrolyte which may enter the vent cap to ensure that it is returned to the battery cell and does not flow through the vent cap to the exhaust gas port or become entrained in the flow of gases passing through the vent cap. The invention also relates to a vent cap assembly for partial insertion in the battery fill tubes to facilitate cleaning the battery cover surface area under the vent cap assembly without permitting cleaning fluid to enter the battery housing, and for full insertion in the battery fill tubes after cleaning.
2. Description of Related Art
Conventional lead-acid batteries, such as those used in automotive applications, generally include a number of cells disposed in a battery housing. Each cell typically includes a plurality of positive and negative battery plates or electrodes. Separators are sandwiched between the plates to prevent shorting and undesirable electron flow produced during the reaction occurring in the battery. The plates and separators are immersed in a liquid electrolyte in the cell, the most common being aqueous sulfuric acid. The positive plate generally is constructed of a lead-alloy grid covered with lead oxide, while the negative plate generally contains lead as the active material, again covering a lead-alloy grid.
The electromotive potential of each battery cell is determined by the chemical composition of the electro-active substrates employed in the electrochemical reactions. For lead-acid batteries, such as those described above, the potential is usually about two volts per cell, regardless of cell volume. Since vehicles manufactured by original equipment manufacturers (OEMs) typically require 12-volt batteries, most automotive batteries include six cells (6 cellsxc3x972 volts per cell=12 volts). The size of the housing for the battery is selected based on the packaging constraints of a particular vehicle, i.e., the physical dimensions defined by the vehicle manufacturer for containment of the battery in the engine compartment.
In most battery constructions the battery housing includes a box-like base containing the cell and is made of a moldable resin. The housing is generally rectangular in horizontal cross section, the cells being provided by vertical partitions within the housing. A cover is provided for the casing, the cover includes terminal bushings and a series of fill tubes to allow electrolyte to be added to the cells and to permit servicing, if required, during the life of the battery. To prevent undesirable spillage of electrolyte from the fill tubes, and to permit exhausting of gases generated during the electrochemical reaction, batteries have included some sort of filler hole cap and/or vent cap assemblies. Battery electrolyte spillage can be caused by a number of factors, including vibration or tilting as the vehicle with which the battery is used maneuvers during normal use. Electrolyte escape may also be caused by battery overheating, a problem especially pronounced in recent years with smaller car engines which tend to create an adverse thermal environment around the battery.
In addition to preventing spillage of electrolyte from the cells, the design of the battery cover and filler caps need to perform an important and different function, namely exhaust of gases generated during the electrochemical reaction. More specifically, gases are liberated from lead-acid batteries during the charge and discharge reactions. Such reactions start at the time the battery is originally charged (called xe2x80x9cformationxe2x80x9d) by the manufacturer or by the retailer or vehicle manufacturer. They also occur during normal operating use of the battery. Factors such as high current charge and discharge conditions, and changes in temperature, can affect the rate at which gas evolution occurs. The gas generation and evolution issues in lead-acid battery construction are particularly important because the liberated gases are hydrogen and oxygen, and it is important to vent such gases in a controlled way from the battery to prevent pressure build-ups in the housing which could lead to electrolyte leaks, housing failures or, most significantly, explosions within the housing.
Electrolyte spillage and gas evolution are interrelated and equally important in the construction of an effective vent cap system. For example, electrolyte may enter the vent cap through several mechanisms. One mechanism is through vibrational or tilting spray of electrolyte into the cap, and another is through a mechanism frequently referred to as xe2x80x9cpumping.xe2x80x9d The latter occurs when gas evolved in the battery bubbles from the cells and carries or forces electrolyte out the fill tube and into the cap. Upon entering the cap, the electrolyte may be carried out the exhaust passage to cause damage to external battery components such as the battery terminals or adjacent engine components.
OEMs have recognized the importance of the dual function performed by the vent caps and have instituted a number of testing specifications designed to ensure electrolyte retention within the cells of the battery. One such test involves tilting a battery thirty-five degrees (35xc2x0) about the longitudinal center line of the battery. While a number of different solutions have been proposed to provide an effective vent cap system, optimization has still not been achieved in one vent cap due to numerous demands with which the battery designer is facedxe2x80x94ensuring adequate electrolyte return, condensation, reducing electrolyte in the exhaust flow, pumping of electrolyte through the vent cap system and tilting of the battery. All of these factors can result in electrolyte loss.
An improved vent cap system for minimizing the possibility of electrolyte leakage from the battery and efficiently directing gases from the battery is still needed. Such an improved vent cap would represent a substantial advance in the art.
The current process for installing the battery vent cap assemblies also presents a problem. In order to understand the problem, it is first necessary to review part of the process for manufacturing a battery. Initially, the battery housing, including its cover, is provided containing the battery cells. The battery housing is submerged in acidic electrolyte fluid in order to fill the battery housing with electrolyte fluid through the fill tube holes in the battery cover. After filling the battery housing with electrolyte fluid, the battery is removed from the electrolyte fluid; however, some residual electrolyte fluid usually remains on external surfaces of the battery housing, and oftentimes, dust and other debris associated with the manufacturing environment adhere to the residual electrolyte fluid coating on the battery housing external surfaces. The residual electrolyte fluid coating, dust, and other debris must be washed away to prepare the battery for shipment. Before washing the battery housing external surfaces, the fill tube holes must be plugged to prevent washing fluid from entering the battery housing.
In the present practice (as depicted in FIG. 10), the fill tube holes are temporarily capped with what those skilled in the art refer to as xe2x80x9cwork-in-process ventsxe2x80x9d or xe2x80x9cin-process vents.xe2x80x9d FIG. 12 shows a common in-process vent 300 inserted in a fill tube hole of battery cover 316. In-process vent 300 prevents electrolyte spillage and permits evolution of subsequently generated gases within the battery housing. In-process vent 300 includes an upper portion 312 and a protruding member 314 extending from a bottom surface of upper portion 312. Gases generated within the battery housing pass through protruding member 314 to upper portion 312 where the gases are vented from the battery housing. FIG. 12 shows only one protruding member 314 for in-process vent 300; however, in-process vent 300 includes a protruding member 314 for insertion into each fill tube hole in battery cover 316. With the in-process vents 300 installed, the external surfaces of the battery housing are washed in order to remove electrolyte fluid and other debris from the battery housing surfaces. The bottom surface of upper portion 312 is far enough above the surface of battery cover 316 to permit washing the battery cover surface located beneath in-process vent 300.
Following the initial wash stage, the battery cells are charged in a process known as formation. Heat generated during formation oftentimes causes evaporation of some of the electrolyte fluid which is exhausted through the in-process vents 300. If needed, the in-process vents 300 are removed and additional electrolyte fluid is added through the fill tube holes in order to top off the battery electrolyte fluid level. Then, the in-process vents 300 are reinstalled and the battery cells are charged again in order to attain a fully charged battery. The in-process vents 300 are removed once more in order to facilitate topping off electrolyte fluid level, if necessary. At this point, the battery cells are fully charged, and the electrolyte level is optimum, but before the production vent cap assemblies are installed to complete production of the battery, the external surfaces of the battery housing and cover 316 are cleaned again in order to remove any residual electrolyte fluid and any other debris. The present approach for this process is depicted in FIG. 10. In the prior art process, the protruding members 314 for the in-process vents 300 are inserted into the fill tube holes in the battery cover 316. Then, the battery is typically removed to a washing-type machine. Following washing and rinsing of the external surfaces of the battery housing and cover 316, the battery is moved to a drying-type machine. Following drying, the in-process vents 300 are removed and final, production vent cap assemblies are inserted to complete production of the battery. The problem with the prior art approach is that it requires the use of additional labor, cost, and time to install the in-process vents 300, wash the battery, dry the battery, remove the in-process vents 300, and then install the final vent cap assemblies.
An improved vent cap assembly obviating the prior practice of having to use in-process vents 300 to prevent cleaning fluid from entering the battery housing during the final washing of the housing is needed. Such an improved vent cap assembly would represent a significant advance in the art.
The present invention provides a vent cap system which includes a one-piece or two-piece construction adapted to facilitate electrolyte return to the battery, minimize electrolyte entrainment of the exhaust flow path, distribution of electrolyte to a plurality of battery cells to maintain desirable electrolyte level and an improved barrel construction. More particularly, the vent cap sealing mechanism of the present invention minimizes the escape of gas or electrolytes around the barrel and into the space between the bottom of the vent cap and the battery cover.
The present invention also features a vent cap in which any electrolyte flow into the cap is redirected back to a cell of the battery, while gases escaping from the battery are directed to a gas outlet through a tortuous but effective gas flow path. These particular features are also accomplished in various battery orientations, including orientations in which the battery is tilted significantly about its longitudinal axis.
The present invention also features a vent cap having internal baffles constructed and arranged to prevent accumulation of pockets of electrolyte within the cap and an attenuation element entry port arranged and constructed to minimize intrusion of electrolyte.
These and other features will become apparent from the following detailed description of the preferred embodiment, taken in conjunction with the figures. Generally, however, they are accomplished by providing a vent cap system having a ganged arrangement for three battery fill tubes and including molded thermal plastic component. The vent cap includes three aligned splash barrels to be inserted in the battery fill tubes, each including a lower central aperture, breather holes about the central aperture and an external ring flange surrounding the barrel to act as a fluid tight seal between the barrels and the fill tubes.
In one preferred embodiment, the vent cap includes a top and bottom component. Barrels extend from an angled floor of the cap of the bottom component adjacent an edge thereof so that any electrolyte entering the cap will flow toward the aligned and spaced apart barrel openings. Barriers are provided about the barrel openings to prevent pockets of electrolyte from accumulating in the cap. The lower component also includes the bottom portion of a flame arrester housing which itself includes an entry chamber. The top component includes downwardly directed tubes or splash guards having open bottoms and being arranged to be coaxial with but spaced slightly above the barrel openings when the top and bottom components are assembled. The top component also includes the upper portion of the flame arrester housing including a cup for receiving the preferred micro-porous material, and the entry chamber. The latter is open to provide a pathway for the escape of gases through the arrester and out of an exhaust port provided in the upper compartment. The opening to the arrester housing is optimally located in the upper half of the vent cap and above the center line of the barrel openings.
Another embodiment of the present invention provides a vent cap assembly for a battery of the type having electrolyte therein. The vent cap assembly comprises a top portion, and a vent cylinder extending downwardly from the top portion and arranged to be inserted into a fill tube of a battery housing. The vent cylinder includes a first portion forming a first interference fit between the first portion and the fill tube when the vent cylinder is partially inserted in the fill tube sufficient to prevent fluid from entering the fill tube, and further including a second portion forming a second interference fit between the second portion and the fill tube when the vent cylinder is fully inserted in the fill tube. The magnitude of interference for the second interference fit is greater than the magnitude of interference for the first interference fit. When the vent cylinder is partially inserted in the fill tube, spacing exists between a top surface of the battery housing and a bottom surface of the top portion to permit washing and drying the top surface of the battery housing located beneath the top portion of the vent cap assembly.
The second portion comprises a ring flange formed on an outer wall of the vent cylinder having a radial thickness formed on the vent cylinder such that the second interference fit exists between the ring flange and the fill tube, and the vent cylinder is insertable within the fill tube such that the ring flange deforms to create a ring seal between the vent cylinder and the fill tube. The ring flange and the fill tube may deform to create a ring seal between the vent cylinder and the fill tube. The second interference fit is in the range between seven thousandths and forty thousandths of an inch (0.007xe2x80x3-0.040xe2x80x3). The ring flange comprises a trailing portion formed on a first end of the ring flange adjacent to the top portion, and a leading portion formed on an end of the ring flange opposite the first end thereof. The leading portion and the trailing portion intersect to form an apex that is slightly rounded to provide a smooth transition between the leading portion and the trailing portion. The leading portion includes a first sloped face having an angular orientation in the range between twenty degrees and forty degrees (20xc2x0-40xc2x0) relative to the outer wall of the vent cylinder, and the trailing portion includes a second sloped face having an angular orientation in the range between ninety-five degrees and one hundred and fifteen degrees (95xc2x0-115xc2x0) relative to the outer wall of the vent cylinder. The first portion comprises a member coupled to and extending down from the ring flange, and the member has a tubular shape.
Another embodiment of the present invention provides a method for removing electrolyte fluid and debris adhering to external surfaces of a battery comprising the steps of filling the battery with the electrolyte fluid, fully charging the battery, partially inserting vent cylinders of a vent cap assembly into fill tubes of the battery to form a first interference fit between each vent cylinder and each fill tube sufficient to permit washing the external surfaces without allowing washing fluid to enter the fill tubes, and fully inserting the vent cylinders of the vent cap assembly into the fill tubes to form a second interference fit between each vent cylinder and each fill tube. The method further includes the steps of washing the external surfaces, including a surface located beneath the vent cap assembly, while the vent cap assembly is partially inserted; and drying the external surfaces.
The improved vent cap assembly and its method of use obviate the prior practice of having to use of an in-process vent during battery washing before a final, production vent cap assembly could be inserted into the battery housing. Specifically, the improved vent cap assembly is partially inserted into the battery housing during battery washing, and then completely inserted to ready the battery use.
Other ways in which the vent cap (and the vent cap assembly and its method of use) of the present invention, or modifications thereof, provide the features mentioned above, and other improvements over the prior art, will become apparent to one of ordinary skill in the art after reading the balance of the specification and after reviewing the drawings. Such other ways and modifications are deemed to be within the scope of the present invention.